The present invention relates to an optical data recording and reproducing apparatus and a method thereof, and an optical storage medium, such as a CD (Compact Disc) and DVD (Digital Video Disc, Digital Versatile Disc) for storing data which are recorded and reproduced by the apparatus and method.
Phase-change recording to record signals on optical storage media such as PDs and DVD-RAMs employs a laser beam that is irradiated on each optical storage medium to change a state of a recording layer of the optical storage medium from an amorphous state to a crystalline state and vise-versa.
Such phase-change recording type optical storage media are in the amorphous state just after layer formation. The amorphous state exhibits a low reflectivity as shown in FIG. 1 and hence a problem lies in picking up the laser beam reflected from the recording layer.
In order to solve the problem, a laser beam is irradiated on the optical storage media to raise a temperature of the recording layer to a temperature Tx at which the recording layer is in the crystalline state. The irradiation changes the recording layer from the amorphous state to the crystalline state that exhibits a high reflectivity as shown in FIG. 1 with no difficulty in picking up the reflected laser beam.
The laser beam is again irradiated on the optical storage media to raise a temperature of the recording laser higher than a temperature Tmp at which the recording layer is in the amorphous state. The irradiation changes the recording layer from the crystalline state to the amorphous state.
As described above, the laser beam is controlled in signal recording so that it exhibits a bottom power to raise the temperature of the recording layer high than the temperature Tx and a peak power to raise the temperature of the recording layer higher than the temperature Tmp.
FIG. 2 illustrates a recording layer of a phase-change recording type optical storage medium D with pits P in the amorphous state while the other portions C in the crystalline state. This amorphous-crystalline state combination enables new signal over-writing on the storage medium D on which other signals have already been recorded.
Reproduction of the recorded signals is done by controlling the laser beam to decrease the temperature of the recording layer lower than the temperature Tx, the laser beam being irradiated on the recording layer and reflected therefrom.
The phase-change recording type rewritable optical storage media with large storage capacity as described above are highly applicable to data communications via optical fibers of high transfer rate and satellites, for example.
Such optical storage media are particularly applicable, for instance, to pay-per-view type video-on-demand service. Under the service, data, for example, containing many movies are compressed and transferred to users and recorded on the user's optical storage medium. Each user pay fees only for the movies they have watched among the recorded many movies.
However, under such service, a software such as a movie that has expired the term for use should be erased from the user's optical storage medium in order to protect copyright of the software.